Latent Tuberculosis Infection

• Objective: To review the diagnosis and treatment of latent tuberculosis infection (LTBI). • Methods: Qualititative assessment of the literature. • Results: One third of the world’s population is latently infected with Mycobacterium tuberculosis. From this pool, approximately 9 million active tuberculosis (TB) cases emerge annually, resulting in 2 to 3 million deaths and making TB the most common cause of death by a single infectious agent in the world. In otherwise healthy individuals with LTBI, the lifetime risk for active TB is 5% within the first year of infection and 5% for the remainder of the lifetime of the individual. Perhaps the single most important host risk factor for reactivation TB is co-infection with HIV, where the estimated rate of reactivation is approximately 5% to 10% per year. Other particularly high-risk individuals include those with upper-lobe fibronodular scarring, recent immigrants from regions endemic for TB, nursing home residents, and persons with silicosis, chronic renal insufficiency, gastrectomy, malnutrition, diabetes mellitus, organ transplantation, or immunosuppressive use. Testing for latent infection involves administering 0.1 mL of 5 tuberculin units of purified protein derivative (or 0.1 mL of 2 tuberculin units of RT-23, available in many places outside the United States) intradermally and measuring the diameter of induration at 48 to 72 hours. There is compelling epidemiologic evidence that treatment for LTBI decreases the development of active TB. The preferred treatment regimen of LTBI is 9 months of isoniazid for those with normal chest radiographs. • Conclusion: Correctly diagnosing and treating individuals with LTBI are important cornerstones to curbing the scourge of TB. “[I]n the treatment of Consumption, . . . in the commencement [it] is easy to cure and difficult to understand; but when it has neither been discovered in due time nor treated upon a proper principle, it becomes easy to understand and difficult to cure.” Niccolo Machiavelli (1469-1527) The World Health Organization estimates that one third of the world’s population is latently infected with Mycobacterium tuberculosis [1]. From this pool, approximately 9 million active tuberculosis (TB) cases emerge annually, resulting in 2 to 3 million deaths and making TB the most common cause of death by a single infectious agent in the world [2]. The AIDS epidemic is responsible for the rise in TB cases in many parts of the world (in approximately 1.5 million active TB cases per year there is co-infection with HIV), and co-infection with both agents contributes significantly to TB-related mortality. 95% of cases of TB occur in the developing world. Annual incidence rates exceed 300 cases per 100,000 persons in much of sub-Saharan Africa, the Indonesian and Philippine archipelagos, Afghanistan, Bolivia, and Peru [1,3]. Areas with the highest incidence include the most populous nations of India (1.9 million cases per year) From the Department of Medicine, National Jewish Medical and Research Center, Denver, CO. INSTRUCTIONS The following article, “Diagnosis and Treatment of Latent Tuberculosis Infection,” is a continuing medical education (CME) article. To earn credit, read the article and complete the CME evaluation form on page 188.